College of Agriculture & Life Sciences Arizona Cooperative Extension University of Arizona Paul Brown Charles Sanchez Kurt Nolte Irrigation Management in Yuma County

The Case Study Report Yuma Agriculture Trends/Transformation Agricultural Water Use Trends Factors Impacting Use Irrigation Management Infrastructure Field Procedures Scheduling Efficiencies Future Research

Agricultural Transformation Declining Production Citrus Cotton Sorghum Stable Production Alfalfa Small Grains Expanded Production Vegetables Leafy Greens Broccoli Cauliflower Melons Sudangrass

Vegetable Production Vegetables 6-Fold Increase Winter-Centric Sep-Mar Multi-Cropped Land 6-Fold Increase Vegetables Crop + 2 nd Vegetable + Wheat Melons Cotton Sudan

Agricultural Water Use Downward Trend Total Delivered Per Acre Fluctuations Salinity Control Act Rise of Vegetables Improved Mgmt.

Rise Of Vegetable Production “Subbing Up” Vegetables Subbing: fields flooded for extended period to ensure uniform germination/stands. Very high water consumption, resulted in higher water tables.

Improved Water/Irrigation Management Sprinklers have replaced subbing as a means of establishing vegetable crops. Water used to establish vegetable crops has decreased by 50-75%.

Multi-Crop Production Systems Often Use Less Water

Change in Seasonal Water Use Lower Summer Use Less Cotton & Alfalfa Wheat Matures in Spring Summer Crops Early Termination Vegetable Field Prep Higher Fall Use Vegetable Establishment Vegetable Irrigation Lower Use: Jan/Feb Less Pre-Irrigation

Level Furrow/Basin Irrigation Deep Percolation Root Zone High flows, rapid advance of water limits deep percolation

Level Basin Irrigation Infrastructure, Equipment, Management Lined Canals High Flow Turnouts Laser Leveling (Annual) Press Wheels (Bolas)

Shortened Irrigation Runs Shortened irrigation runs when combined with high flow improve efficiency. Adapted from Sanchez et al Reduced from 1200’ to 600’

Irrigation System Management Sanchez et al. (2008) have developed procedures to optimize irrigation system management in both Valley and Mesa soils. High application efficiencies & uniformity can be achieved using proper inflow rates and cutoff times. Inflow: 22 gpm Cutoff Time: 80 min AE = 0.85 Inflow: 22 gpm Cutoff Time: 80 min DU = 0.94

Drip Irrigation Not Widely Used Advantages Uniform Water Application Reduced Water Use Improved Crop Performance Disadvantages Cost Field Flexibility Salinity Non-Uniform Germination Capacity Limitations N Vegetables: North-SouthMelons: East-West Variable Bed Width Two Row Veg: 42” Cauliflower: 38” Romaine Let: 34” Spring Mix: 84” Level Basins Wheat Alfalfa Sudan

Drip Irrigation Salinity Concerns Salt accumulates above the drip tape and must be flushed out with leaching. Surface or sprinkler irrigation must be used to leach salts from surface soil. Source: Burt et al., 2003 ECe (dS/m)

Salinity Management Leaching is a Requirement! Root Zone Deep Percolation/Lateral Drainage Removes Salt Irrigation Adds Salt -- Leaching requirement: water in excess of ET required to flush salts and maintain proper salinity level in the root zone. -- Varies with salinity of irrigation water and salinity tolerance of crop. Drainage Water

Salinity Management Leaching is a Requirement! Root Zone Deep Percolation/Lateral Drainage Removes Salt Irrigation Adds Salt Drainage Water

Vegetable Crops Intolerant of High Salt Levels Source: Ayers & Wescott, 1994 Late Summer Leaching Prior To Planting Vegetables Leaching fractions of ~15% are required to maintain optimal salinity levels for vegetables.

Fallowing & Salinity From: Ayers & Wescott, 1994 Data: Mohamed & Amer, 1972 Saline Groundwater Water Moves to Surface By Capillarity Evaporation Salt Accumulation

Irrigation Scheduling Understanding Soil Water Reservoir -Field Capacity -Wilting Point -Allowed Depletion Unavailable Plant Stress Readily Available We Manage ~ 25% of Soil Water Through Irrigation |-Plant Available Water-|

Estimating Crop Water Use ETos Weather Data Crop Water Use Reference Evapotranspiration Crop Coefficients Crop Coefficients AZMET Reference ET

Estimating Crop Water Use ETos Crop Coefficients Reference Evapotranspiration Lysimeters Measured Water Use vs Reference ET Measure Water UseWater Use as Fraction of Reference ET

District Wide Irrigation Efficiency Wellton-Mohawk Irrigation & Drainage District Procedure 1 Crop Water Use Crop ET * Acreage Compared to Water Diverted to Farms Procedure 2 Salinity of Water Diverted to District (Ciw) Salinity of Water Diverted to Drainage Canal (Cdw) LF = Ciw/Cdw Efficiency = 100*(1-LF)

On-Farm Irrigation Efficiency From Crop Water Use Estimates Without acreage adjustment: 60-70% With acreage adjustments: 70-76%

District Irrigation Efficiency Using Salt Balance Procedures -Irrigation efficiencies averaging close to 75%, upward trend -Seasonal minimum during vegetable establishment -Peak efficiencies in summer (deeper rooted crops)

Improving Water Use Efficiency Growers Implementing New Production Technologies Yield/Acre-Inch of Evapotranspiration

Research Needs Reexamine Crop Water Use Much of Data Very Old! New Vegetable Crops/Production Strategies Salinity Issues Effectiveness of Current Leaching Procedures Fallow/Salinity Assessment Sprinkler Management Microclimate, Salinity & Crop Establishment Scientific Irrigation Scheduling Weather/ET Systems Soil Moisture Monitoring